[Bug libstdc++/95904] Improve the diagnostic for conflicting return types in std::visit

[cvs-commit at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95904

--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Ville Voutilainen <vi...@gcc.gnu.org>:

https://gcc.gnu.org/g:3427e31331677ca826c5588c87924214f7e5c54b

commit r11-3760-g3427e31331677ca826c5588c87924214f7e5c54b
Author: Ville Voutilainen <ville.voutilai...@gmail.com>
Date:   Fri Oct 9 20:47:01 2020 +0300

    libstdc++: Diagnose visitors with different return types [PR95904]

    libstdc++-v3/ChangeLog:

            PR libstdc++/95904
            * include/std/variant (__deduce_visit_result): Add a nested ::type.
            (__gen_vtable_impl</*base case*/>::_S_apply):
            Check the visitor return type.
            (__same_types): New.
            (__check_visitor_result): Likewise.
            (__check_visitor_results): Likewise.
            (visit(_Visitor&&, _Variants&&...)): Use __check_visitor_results
            in case we're visiting just one variant.
            * testsuite/20_util/variant/visit_neg.cc: Adjust.